1. Field of the Invention
The present invention relates to an inspection apparatus inspecting defects or the like of a pattern formed on the surface of an inspection object using an electron beam, and particularly relates to an inspection apparatus irradiating an electron beam to the inspection object and capturing secondary electrons modified according to properties of the surface thereof to form image data, and inspecting in high throughput a pattern or the like formed on the surface of the inspection object based on the image data, and a device production process of producing a device in a high yield using the inspection apparatus as used for detection of wafer defects in semiconductor manufacturing. More specifically, the present invention relates to a detection apparatus with a projection electron microscope system using broad beams, and a device production process using the apparatus.
In a semiconductor process, the design rule is about to move into an era of 100 nm, and the type of production is now making a transition from low variety and large production represented by DRAM to high variety and small production found in SOC (Silicon on chip). Accordingly, the number of production steps increases, improvement in yield for each step becomes essential, and inspection of defects coming from the process becomes important. The present invention relates to an apparatus for use in inspection of a wafer or the like after each step in the semiconductor process, and relates to an inspection process and apparatus using an electron beam or a device production process using the same.
2. Description of the Related Art
As semiconductor devices is highly integrated, and patterns becomes finer, a high resolution and high throughput inspection apparatus is required. For inspecting defects of a wafer substrate having a 100 nm design rule, pattern defects or defects of particle vias in wiring having a line width of 100 nm or smaller and electric defects thereof should be observed, and hence a resolution of 100 nm or lower is required, and the inspection quantity increases due to an increase in the number of production steps resulting from high integration of the device, and therefore high throughput is required. Furthermore, as the device is increasingly multilayered, the inspection apparatus is required to have a function of detecting a contact failure (electric defects) of vias for connection of wiring between layers. Currently, optical defect inspection apparatuses are mainly used, but defect inspection apparatuses using electron beams are expected to go mainstream in stead of the optical defect inspection apparatus in terms of resolution and inspection of contact failure. However, the electron beam-type defect inspection apparatus has a disadvantage, i.e. it is inferior in throughput to the optical type.
Thus, development of an inspection apparatus having a high resolution and high throughput and being capable of detecting electric detects is required. It is said that the resolution of the optical type is maximum ½ of the wavelength of light used, which is equivalent to about 0.2 μm for commercially practical visible light, for example.
On the other hand, for the type using an electron beam, a scanning electron beam type (SEM type) is usually commercially available, the resolution is 0.1 μm and the inspection time is 8 hours/wafer (200 mm wafer). The electron beam type has a remarkable characteristic such that electric defects (breakage of wiring, poor conduction, poor conduction of vias and the like) can be inspected, but the inspection speed is very low, and development of a defect inspection apparatus performing inspection at a high speed is expected.
Generally, the inspection apparatus is expensive, inferior in throughput to other process apparatuses, and is therefore used after an important step, for example, etching, film formation, or CMP (chemical mechanical polishing) planarization processing under present circumstances.
The inspection apparatus of the scanning type using an electron beam (SEM) will be described. The SEM type inspection apparatus reduces the size of an electron beam (the beam diameter corresponds to the resolution), and scans the beam to irradiate a sample in a line form. On the other hand, a stage is moved in a direction perpendicular to the scanning direction of the electron beam to irradiate an observation area with the electron beam in a plain form. The scan width of the electron beam is generally several hundreds μm. Secondary electrons generated from the sample by irradiation with the size-reduced electron beam (refereed to as primary electron beam) are detected with a detector (scintillator+photomultiplier (photomultiplier tube) or a semiconductor-type detector (PIN diode type) or the like). Coordinates of the irradiation position and the amount of secondary electrons (signal intensity) are synthesized into an image, and the image is stored in a storage device, or outputted onto a CRT (cathode ray tube). The principle of the SEM (scanning electron microscope) has been described above, and defects of a semiconductor (usually Si) wafer in a step on progress are detected from the image obtained by this process. The inspection speed (corresponding to throughput) depends on the amount of primary electron beams (current value), the beam diameter and the response speed of the detector. 0.1 μm of beam diameter (that can be considered as resolution), 100 nA of current value and 100 MHz of detector response speed are maximum values at present and in this case, it is said that the inspection speed is about 8 hours per wafer having a diameter of 20 cm. The serious problem is that this inspection speed is very low compared to the optical type ( 1/20 or less of that of the optical type). Particularly, pattern defects and electric defects of a device pattern of a design rule of 100 nm or smaller formed on the wafer, i.e. of a line width of 100 nm, a via with the diameter of 100 nm or smaller and the like, and a contaminant of 100 nm or smaller can be detected at a high speed.
For the SEM-type inspection apparatus described above, the above inspection speed is considered as a limit, and a new type of inspection apparatus is required for further enhancing the speed, i.e. increasing the throughput.